X-ray tube and method of producing the same

ABSTRACT

An X-ray tube  1  comprises of a bulb  10  joined to an envelope main body  4  at one end side thereof and having an inner cylinder portion  10   a  extending inwardly at the other end side thereof, a metal tube  11  having an extension portion  11   a  abutting against the inner cylinder portion  10   a  on the outer periphery of one end side thereof and projecting to the outside of the bulb  10  through the inner cylinder portion  10   a  at the other end side thereof, and a target supporter  12  supporting a target T at the one end side thereof and inserted into the metal tube  11  at the other side thereof. The inner cylinder portion  10   a  of the bulb  10  and the extension portion  11   a  of the metal tube  11  are fuse-bonded to each other, and the target supporter  12  is welded to the end portion of the metal tube  11  projecting from the bulb  10.

FIELD OF THE ART

The present invention relates to an X-ray tube and a method for makingthe X-ray tube, and particularly to a micro-focus X-ray tube in which anX-ray focus point can be remarkably finely set, and a method for makingthe X-ray tube.

BACKGROUND ART

An X-ray tube outputs X-rays by inpinging electrons on a target, andconventionally has been utilized as an X-ray generator such as an X-rayinspection apparatus or the like which is used for nondestructiveinspection, non-contact inspection or the like. For a sample of SuchX-ray tube, one disclosed in Japanese Unexamined Examined Utility ModelApplication No. H03-110753 is well known. The X-ray tube described inthis publication has a vacuum envelope molded insulating material suchas glass or the like in a substantially cylindrical shape. Both endportions of the vacuum envelope are inwardly folded over the overallperipheries thereof, and thus inner cylinder portions extending to theinside of the envelope are formed at both ends of the vacuum envelope.An electron generating unit containing a cathode filament, a focuselectrode, etc., are fixed in one inner cylinder portion. Furthermore, ametal tube is fuse-bonded to the other folded portion. A targetsupporter for supporting a target is fixed to the metal tube.Accordingly, the electron generating unit and the target oppose eachother.

Recently, in order to enhance the sharpness and magnification of aradioscopy image shooting by an X-ray inspection apparatus or the like,it has been required to reduce the dimension (diameter) of the X-rayfocus point in the X-ray tube to a smaller point. Therefore, needs for aso-called micro-focus X-ray tube which can set the X-ray focus point toan extremely small point has been increasingly grown. In order to setthe X-ray focus point to an extremely small point as described above, itis required to mount a target receiving electrons to a vacuum envelopeaccurately.

DISCLOSURE OF THE INVENTION

However, it has been difficult to secure the metal tube to the vacuumenvelope accurately when the inner cylinder portion and the metal tubeare fuse-bonded to each other in the conventional X-ray tube asdescribed above. Furthermore, in the conventional X-ray tube, the metaltube and the target supporter can be fixed to each other in the vacuumenvelope. Therefore, much effort is needed to fix the target supporterto the metal tube accurately. As described above, it has been difficultin the conventional X-ray tube to set the X-ray focus point to anextremely small point due to the dimensional accuracy and fabricationaccuracy in the making process.

Therefore, the present invention has an object to provide an X-ray tubein which respective components are fabricated accurately and the X-rayfocus point can be set to an extremely small point, and a method formaking an X-ray tube which can easily make an X-ray tube in which theX-ray focus point can be set to an extremely small point whileremarkably keeping the dimension accuracy and the fabrication accuracyin the making process.

In order to achieve the above object, an X-ray tube is an X-ray tube forimpinging electrons emitted from an electron generating unit on a targetand outputting X-rays, comprising an envelope main body having anaccommodation portion for accommodating the electron generating unit; aninsulating bulb joined to the envelope at one end side thereof andhaving an inner cylinder portion extending inwardly at the other endside thereof, a metal tube having an extension fuse bonded to the innercylinder portion on the outer periphery of one end side thereof andprojecting outwardly from the valve through the inner cylinder portionat the other end side thereof, and a target supporter supporting atarget at one end side thereof, inserted through the metal tube at theother side thereof and fuse-bonded to the end portion of the metal tube.

The X-ray tube impinging electrons are emitted from an electrongenerating unit on a target to output X-rays. Therefore, the X-ray tubecomprises an electron generating unit containing a cathode forgenerating electrons, etc., a target as an anode and a target supporterfor supporting the target. Furthermore, the X-ray tube is provided withan envelope main body and a bulb. The envelope main body and the bulbconstitute the vacuum envelope accommodating the electron generatingunit, the target, etc.

The envelope main body has an accommodation portion for accommodatingthe electron generating unit. The bulb is designed in a substantiallycylindrical shape by insulating material such as glass, ceramic or thelike, and one end side thereof is joined to the envelope main body. Aninner cylinder portion extending inwardly is provided at the other endportion of the bulb. That is, the other end portion of the bulb isfolded inwardly over the overall periphery so that a hole portion isformed at the center portion. A metal tube for fixing the targetsupporter is secured to the bulb.

The metal tube is provided at one end side thereof with an extensionportion which can abut against the inner cylinder portion of the bulb.That is, one end portion of the metal tube is folded outwardly over theoverall periphery and a cylinder portion having substantially the samediameter as the inner cylinder portion of the bulb is formed on theouter periphery of one end side of the metal tube. Furthermore, theother end side of the metal tube can be inserted through the innercylinder portion of the bulb. In addition, the other end side of thetarget supporter for supporting the target can be inserted through themetal tube.

The X-ray tube comprising the above components according to the presentinvention is made according to the following procedure. In this case,the metal tube is secured to the bulb previously. When the metal tube issecured to the bulb, (the end face of) the inner cylinder portion and(the end face of) the extension portion of the metal tube arefuse-bonded to each other under a state where the metal tube isprojected from the inner cylinder portion to the outside of the bulb. Atthis time, the metal tube can be reliably positioned in the bulb, andthus both can be fuse-bonded to each other accurately.

For example, after the bulb is joined to the envelope main body, thetarget supporter is welded to the end portion of the metal tubeprojecting from the bulb while the other end of the target supporter(the end portion of the target supporter at which the target is notsupported) is inserted into the metal tube fixed to the bulb. At thistime, the target supporter is slid relatively to the metal tube while ajig, an optical position sensor or the like is used, whereby thesecuring position of the target can be determined accurately. The workof welding the target supporter to the metal tube can be easilyperformed from the outside of the bulb, and thus the target supporterand the metal tube can be firmly fixed to each other accurately. Inaddition, the inside of the vacuum envelope comprising the envelope mainbody and the bulb can be kept air-tight.

As described above, in the X-ray tube of the present invention, therespective components can be fabricated while positioned with extremelyhigh accuracy, and the positional relationship between the electrongenerating unit and the target is determined accurately. Accordingly,according to the X-ray tube, the X-ray focus point can be set to anextremely small point.

In an X-ray tube making method according to the present invention, anx-ray tube for impinging electrons emitted from an electron generatingunit accommodated in an envelope main body on a target supported by atarget supporter to output X-rays, by using a bulb having aninwardly-extending inner cylinder portion at the opposite side to theside thereof to be joined to the envelope main body and a metal tubeprovided with an extension portion abutting against the inner cylinderportion of the bulb on the outer periphery thereof and is insertablethrough the inner cylinder portion, the end face of the inner cylinderportion and the extension portion of the metal tube are fuse-bonded toeach other while the metal tube is projected from the inner cylinderportion to the outside of the bulb, the target supporter is insertedinto the metal tube, and the target supporter is welded to the endportion of the metal tube projecting from the bulb.

According to the X-ray tube making method described above, therespective components can be fabricated while remarkably keeping thedimension accuracy and the fabrication accuracy in the manufacturingprocess. Accordingly, when the X-ray tube making method described aboveis used, there can be easily made an X-ray tube in which the X-ray focuspoint can be set to an extremely small point.

In this case, when the target supporter is welded to the end portion ofthe metal tube, the target supporter is preferably positioned to themetal tube by using a jig. Furthermore, when the target supporter iswelded to the end portion of the metal tube, the target supporter may bepositioned to the metal tube by using position detecting means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an X-ray tube according to thepresent invention, and

FIG. 2 is a side view thereof;

FIG. 3 is a cross-sectional view showing the construction of an electrongun accommodating portion of the X-ray tube;

FIG. 4 is a cross-sectional view showing a bulb and a metal tubeconstituting the X-ray tube;

FIG. 5 is a flowchart showing an X-ray tube making method according tothe present invention;

FIG. 6 to FIG. 9 are diagrams showing a method for positioning a targetsupporter to a bulb; and

FIG. 10 to FIG. 12 are flowcharts showing another embodiment of theX-ray tube making method according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be describedhereunder in detail with reference to the accompanying drawings. Tofacilitate the comprehension of the explanation, the same referencenumerals denote the same parts, where possible, throughout the drawings,and a repeated explanation will be omitted.

FIG. 1 is a cross-sectional view showing a preferred embodiment of anX-ray tube according to the present invention. The X-ray tube 1 shown inFIG. 1 is suitably used as an X-ray generating source of an X-rayinspection apparatus, for example, and it comprises of a vacuum envelope2, an electron generating unit (electron gun) 3, and a target T. Theelectron generating unit 3 has a cathode C which is a porous tungsten orthe like, impregnated with BaO or the like. The target T is a laminatedX-ray generating films formed of tungsten or the like through aprotection layer on a carbon layer. The electron generating unit 3 andthe target T are accommodated in the vacuum envelope 2, and whenelectrons emitted from the electron generating unit 3 impinge againstthe target T in the vacuum envelope 2, an X-ray is output. As shown inFIG. 1, the vacuum envelope 2 mainly comprises an envelope main body 4and a bulb 10.

The envelope main body 4 comprises a body portion 5 in which the targetT serving as an anode is accommodated, and an electron gun accommodatingportion 6 in which the electron generating unit 3 serving as a cathodeis accommodated. The body portion 5 is formed of metal or the like in acylindrical shape, and has an inner space 5 a. A flange portion 5 bfixed to a housing or the like of the X-ray inspection apparatus (notshown) is provided on the outer periphery of the body portion 5.Furthermore, a lid plate 7 having an output window 7 a is fixed to thelower portion of the body portion 5 in FIG. 1, and one end side of theinner space 5 a is closed by the lid plate 7. The electron gunaccommodating portion 6 is formed in a cylindrical shape so as to have asubstantially rectangular cross-section as shown in FIG. 2, andconnected (fixed) to the lower portion of the side portion of the bodyportion 5. As shown in FIG. 1, the axial center of the body portion 5and the axial center of the electron gun accommodating unit 6 aresubstantially orthogonal to each other, and the inside of the electrongun accommodating portion 6 intercommunicates with the internal space 5a of the body portion 5 through an aperture 6 a.

The electron generating unit 3 accommodated in the electron gunaccommodating portion 6 will be described. As shown in FIG. 1 and FIG.3, the electron generating unit 3 contains a cathode C, a heater 30, afirst grid electrode 31 and a second grid electrode 32. The cathode C,the heater 30, the first grid electrode 31 and the second grid electrode32 are secured to a stem board 34 through plural (eight in thisembodiment) pins 33 a to 33 h extending in parallel. Specifically, thecathode C is secured to the pin 33 a (see FIG. 2) fixed to the stemboard 34, and supplied with electric power from the outside through thepin 33 a. Likewise, the heater 30 is secured to the pins 33 b and 33 c(see FIG. 2) fixed to the stem board 34, and supplied with electricpower from the outside through the pins 33 b and 33 c.

Furthermore, the first grid electrode 31 is secured to the pins 33 d, 33e, 33 f and 33 g fixed to the stem board 34, and supplied with electricpower from the outside through these pins 33 d to 33 g. The second gridelectrode 32 is secured to the pin 33 h fixed to the stem board 34, andsupplied with electric power from the outside through the pin 33 h. Asdescribed above, the electron generating unit 3 in which the cathode C,etc., are unified to the stem board 34 is inserted from the end portionat the opposite side to the aperture 6 a into the electron gunaccommodating portion 6, and the stem board 34 is fixed to the endportion of the electron gun accommodating portion 6.

The bulb 10 constituting the vacuum envelope 2 in combination with theenvelope main body 4 is formed of insulating material such as glass,ceramic or the like in a substantially cylindrical shape. As shown inFIG. 1, a ring member 8 formed of metal or the like is fuse-bonded toone end side (the lower end side in FIG. 1) of the bulb 10. The ringmember 8 is joined (welded) to the body portion 5 constituting theenvelope main body 4. As described above, one end side of the bulb 10 isjoined to the envelope main body 4.

On the other hand, as shown in FIG. 1 and FIG. 4, an inner cylinderportion 10 a having a cylindrical shape extending inwardly is providedon the other end side (the upper end side in FIG. 1 and FIG. 4) of thebulb 10. That is, the other end portion (upper end portion) of the bulb10 is folded inwardly across the overall periphery thereof so that ahole portion is sectionally formed at the center portion, whereby theother end side of the bulb 10 is opened to the outside through theinside of the inner cylinder portion 10 a. The metal tube 11 forsupporting the target T in the body portion 5 is secured to the innercylinder portion 10 a of the bulb 10.

As shown in FIG. 4, the metal tube 11 basically has an outer diametersmaller than the inner diameter of the inner cylinder portion 10 a ofthe bulb 10. The metal tube 11 also has an extension portion 11 a on theouter periphery at one end side thereof (the lower end side in FIG. 4).That is, the one end portion of the metal tube 11 is outwardly foldedover the overall periphery thereof, and a cylindrical portion (outercylinder portion) having substantially the same diameter as the innercylinder portion 10 a of the bulb 10 is formed on the outer periphery atthe one end side of the metal tube 11. The other end side (the upper endside in FIG. 4) of the metal tube 11 can be inserted into the innercylinder portion 10 a of the bulb 10.

When the other end side of the metal tube 11 is being inserted into theinner cylinder portion 10 a of the bulb 10, the end face of theextension portion 11 a abuts against the end face of the inner cylinderportion 10 a equipped to the bulb 10. When the extension portion 11 aabuts against the inner cylinder portion 10 a, the other end portion ofthe metal tube 11 is projected outwardly from the bulb 10 through theinner cylinder portion 10 a as shown in FIG. 1. The end face of the bulb10 and the end face of the extension portion 11 a are fuse-bonded toeach other.

Into the metal tube 11 secured to the bulb 10 as described above, theother end side of the target supporter 12 for supporting the target T atone end side thereof is inserted. The target supporter 12 is formed ofcopper material or the like in a rod shape, and a slant surface 12 a(see FIG. 1) which is inclined so as to be far from the electrongenerating unit 3 as approaching from the bulb 10 side to the bodyportion 5 side (in FIG. 1, from the upper side to the lower side) isprovided at one end side (the lower end side in FIG. 1) of the targetsupporter 12. The target T is embedded at the end portion of the targetsupporter 12 so that the surface thereof is aligned with the slantsurface 12 a.

The other end portion (the upper end portion in FIG. 1) of the targetsupporter 12 is welded to the end portion of the metal tube 11projecting from the bulb 10, whereby the target supporter 12 extendssubstantially in parallel to the axial centers of the bulb 10 and thebody portion 5, and also it is substantially orthogonal to the traveldirection of electrons from the electron generating unit 3. Accordingly,when electrons emitted from the electron generating unit (electron gun)3 impinge against the target T in the vacuum envelope 2, an X-ray isoutput from the surface of the target T in a direction substantiallyorthogonal to the travel direction of the electrons. The X-ray isdischarged to the outside through the output window 7 a covering theopen end (the end portion at the opposite side to the bulb 10 side) ofthe body portion 5. A cover electrode 14 is mounted so as to cover thefuse-bonded portion between the inner cylinder portion 10 a and theextension portion 11 a of the metal tube 11 in the bulb 10.

Next, the method for manufacturing the X-ray tube 1 constructed asdescribed above, that is, the X-ray tube making method according to thepresent invention will be described. When the X-ray tube 1 comprisingthe above-described components according to the present invention isfabricated, the body portion 5 and the electron gun accommodatingportion 6 are joined to each other to fabricate the outer envelope mainbody 4 at a predetermined stage, and also the metal tube 11 is securedto the bulb 10 previously. When the metal tube 11 is secured to the bulb10, the end face of the inner cylinder portion 10 a and the end face ofthe extension portion 11 a of the metal tube 11 are fuse-bonded to eachother under a state where the metal tube 11 is projected from the innercylinder portion 10 a to the outside of the bulb 10. At this time, theend portion of the bulb 10 at the opposite side to the inner cylinderportion 10 a is perfectly opened (see FIG. 4), and thus the metal tube11 can be easily and accurately positioned in the bulb 10. Accordingly,the bulb 10 and the metal tube 11 can be fuse-bonded to each other whilethey are positioned to each other accurately.

Thereafter, the respective components are assembled according to theprocedure shown in FIG. 5. That is, first, the bulb 10 securing themetal tube 11 and the envelope main body 4 are joined to each other(S10). In this case, the ring member 8 which is fuse-bonded to the bulb10 previously is welded to the envelope main body 4 (body portion 5).Subsequently, the bulb 10 is joined to the envelope main body 4, and theother end of the target supporter 12 (the end portion of the targetsupporter 12 at which the target T is not supported) is inserted intothe metal tube 11 fixed to the bulb 10, and under this state, the targetsupporter 12 is positioned to the bulb 10. Furthermore, the targetsupporter 12 is welded to the end portion of the metal tube 11projecting from the bulb 10 (S12).

Here, when the target supporter 12 is positioned to the bulb 10 (metaltube 11), jigs as shown in FIG. 6 and FIG. 7 are preferably used. A jig60 shown in FIG. 6 can be engangedly fitted in the inner space 5 a ofthe body portion constituting the envelope main body 4 from the open endat the opposite side to the bulb 10. When the jig 60 is fitted in theinner space 5 a of the body portion 5, the jig 60 is fitted to the endportion of the target supporter 12 inserted into the metal tube 11 sothat the target T is located at a predetermined mount place. That is,the jig 60 has a slant surface 61 abutting against the slant surface 12a of the target supporter 12 and a regulating surface 62 abuttingagainst the end face 12 b of the target supporter 12.

A jig 70 shown in FIG. 7 can be inserted into the inner space 5 a of thebody portion 5 constituting the envelope main body 4 from the open endof the electron gun accommodating portion 6. When the jig 70 is insertedinto the inner space 5 a of the body portion 5 so as to be in parallelto the axial center of the electron gun accommodating portion 6, the jig70 is fitted to the end portion of the target supporter 12 inserted intothe metal tube 11 so that the target T is located at a predeterminedmount place. That is, the jig 70 has a slant surface 71 abutting againstthe slant surface 12 a of the target supporter 12 and a regulatingsurface 72 abutting against the end face 12 b of the target supporter12.

When the target supporter 12 is positioned to the bulb 10, an opticalposition sensor 80 (position detecting means) as shown in FIG. 8 andFIG. 9 may be used. When the target supporter 12 is positioned to thebulb 10 (metal tube 11) by using such an optical position sensor 80, theenvelope main body 4 and the bulb 10 are mounted on the horizontal planeH so that the axial center of the bulb 10 and the metal tube 11 islocated vertically. In the case as shown in FIG. 8, measurement light isirradiated from the optical position sensor 80 to the end face 12 c ofthe target supporter 12 at the metal tube 11 side and the horizontalplane H. That is, in this case, the target supporter 12 is slid withrespect to the metal tube 11 so that the target T is located at apredetermined mount place while detecting the distance between thehorizontal plane H and the end face 12 c of the target supporter 12.

In the case as shown in FIG. 9, the optical position sensor 80 ispositioned on the horizontal plane H, the measurement light isirradiated from the optical position sensor 80 into the inner space 5 aof the body portion 5 through the electron gun accommodating portion 6.And, in this case, the target supporter 12 is slid with respect to themetal tube 11 so that the target T is located at a predetermined mountplace while detecting the end face 12 b at the target T side of thetarget supporter 12. As described above, the mount position of thetarget T can be determined accurately by using the position detectingmeans such as the jigs 60 and 70, the optical position sensor 80 or thelike and sliding the target supporter 12 relatively to the metal tube11.

In S12, the welding work is carried out after the target supporter 12 isaccurately positioned to the bulb 10 as described above. Here in S12,the work of welding the target supporter 12 to the metal tube 11 can beeasily carried out from the outside of the bulb 10. Accordingly, thetarget supporter 12 and the metal tube 11 can be firmly fixed to eachother accurately, and also the inside of the vacuum envelope 2comprising the envelope main body 4 and the bulb 10 can be reliably keptair-tight. The cover electrode 14 may be mounted in the bulb 10 or fixedto the target supporter 12 before the target supporter 12 is welded tothe metal tube 11.

When the target supporter 12 is fixed to the bulb 10, the electrongenerating unit 3 is inserted into the electron gun accommodatingportion 6, and the stem board 34 is fixed to the electron gunaccommodating portion 6 (S14) so that the envelope is reliably keptair-tight. Furthermore, the lid plate 7 having the output window 7 aformed therein is fixed to the body portion 5 of the envelope main body4 so that the envelope can be reliably kept air-tight (S16), therebycompleting the X-ray tube 1.

As described above, according to the X-ray tube making method accordingto the present invention, the respective components can be fabricatedwhile remarkably keeping the dimension accuracy and the fabricationaccuracy in the making process. Accordingly, by using the X-ray tubemaking method, the positional relationship between the electrongenerating unit 3 and the target T can be set accurately. According tothe X-ray tube 1 made by this method, the X-ray focus point can be setto an extremely small point.

The making procedure of the X-ray tube 1 shown in FIG. 5 is merely anexample, and various modes can be used as the making procedure of theX-ray tube 1. FIG. 10 to FIG. 12 show other making procedures of theX-ray tube 1. In this case, the body portion 5 and the electron gunaccommodating portion 6 are joined to each other to fabricate anenvelope main body 4 at a predetermined stage, and also the metal tube11 is secured to the bulb 10 previously.

In the example shown in FIG. 10, the electron generating unit 3 issecured to the electron gun accommodating portion 6 of the envelope mainbody 4 (S20). The bulb 10 securing the metal tube 11 is fixed to theenvelope main body 4 (S22). When the bulb 10 is fixed to the envelopemain body 4, the target supporter 12 is inserted into the metal tube 11fixed to the bulb 10, positioned and then welded to the metal tube 11(S24). Here, when the work of S24 is started, the electron gunaccommodating portion 6 has been already closed by the stem board 34.Accordingly, when the target supporter 12 is positioned to the bulb 10,the jig 60 shown in FIG. 6 is used or the optical position sensor 80 isused as shown in FIG. 8. Thereafter, the lid plate 7 having the outputwindow 7 a is fixed to the body portion 5 of the envelope main body 4(S26), the X-ray tube 1 is completed.

In the example shown in FIG. 11, the electron generating unit 3 issecured to the electron gun accommodating portion 6 of the envelope mainbody 4 (S30). Subsequently, the lid plate 7 having the output window 7 ais fixed to the body portion 5 of the envelope main body 4 (S32). Whenthe lid plate 7 is fixed to the body portion 5 of the envelope main body4, the bulb 10 fixed the metal tube 11 is fixed to the envelope mainbody 4 (S34). Thereafter, in S36, the target supporter 12 is welded tothe metal tube 11. In this case, the inner space 5 a of the body portion5 has been already closed by the lid plate 7, and the electron gunaccommodating portion 6 has been already closed by the stem board 34.Accordingly, in S36, the target supporter 12 is inserted from theoutside of the bulb 10 into the metal tube 11, and also the targetsupporter 12 is positioned while the optical position sensor 80 is usedas shown in FIG. 8, whereby the X-ray tube 1 is completed.

In the example shown in FIG. 12, the lid plate 7 having the outputwindow 7 a is first fixed to the body portion 5 of the envelope mainbody 4 (S40). Subsequently, the electron generating unit 3 is secured tothe electron gun accommodating portion 6 of the envelope main body 4(S42). When the electron generating unit 3 is mounted to the electrongun accommodating portion 6, the bulb 10 securing the metal tube 11 isfixed to the envelope main body 4 (S44). Thereafter, the targetsupporter 12 is welded to the metal tube 11 (S46). In this case, theinner space 5 a of the body portion 5 has been already closed by the lidplate 7, and the electron gun accommodating portion 6 has been alreadyclosed by the stem board 34. Accordingly, in S46, the target supporter12 is inserted into the metal tube 11 from the outside of the bulb 10,and also the target supporter 12 is positioned while the opticalposition sensor 80 is used as shown in FIG. 8, whereby the X-ray tube 1is completed.

INDUSTRIAL APPLICABILITY

The X-ray tube and the X-ray tube making method according to the presentinvention are suitably used as a micro-focus X-ray tube which can setthe X-ray focus point to an extremely small point, and the method formanufacturing the same.

1. An X-ray tube for impinging electrons emitted from an electrongenerating unit on a target and outputting an X-ray, comprising: anenvelope main body having an accommodation portion for accommodatingsaid electron generating unit; an insulating bulb joined to saidenvelope main body at one end side of said bulb and having an innercylinder portion extending inwardly at the other end side of said bulb;a metal tube having an extension fuse-bonded to the inner cylinderportion on the outer periphery of one end side of said metal tube andprojecting outwardly from said bulb through said inner cylinder portionat the other end side of said metal tube; and a target supportersupporting a target at one end side of said target supporter with theother end side of said target supporter being inserted through saidmetal tube and welded to an end portion of said metal tube projectingoutside of said bulb; wherein the X-ray tube comprises an abuttingportion between the metal tube and the target supporter which is locatedoutside the bulb.
 2. A method of making an X-ray tube for impingingelectrons emitted from an electron generating unit accommodated in anenvelope main body on a target supported by a target supporter in orderto output X-rays, the method comprising the steps of: providing a bulbhaving an inwardly-extending inner cylinder portion at one end side ofsaid bulb that is located opposite the other end side of said bulb whichis to be joined to said envelope main body, and providing a metal tubehaving an extension portion abutting against said inner cylinder portionof said bulb on the outer periphery of said metal tube, said metal tubebeing insertable through said inner cylinder portion; fuse-bonding anend face of said inner cylinder portion and the extension portion ofsaid metal tube to each other while projecting said metal tube from theinner cylinder portion to the outside of said bulb; and inserting saidtarget supporter into said metal tube and welding said target supporterto an end portion of said metal tube projecting outside of said bulb. 3.The X-ray tube making method according to claim 2, wherein when saidtarget supporter is welded to the end portion of said metal tube, thetarget supporter is positioned to said metal tube by using jig.
 4. TheX-ray tube making method according to claim 2, wherein when said targetsupporter is welded to the end portion of said metal tube, said targetsupporter is positioned to said metal tube by using position detectingmeans.
 5. The X-ray tube according to claim 1, wherein an inner diameterof the metal tube is substantially equal to an outer diameter of thetarget supporter.